The present invention relates to a process for the production of suspensions of cyanuric chloride in aqueous liquids, more particularly water.
Cyanuric chloride is an important starting product for the manufacture of herbicides, optical brighteners, reactive dyes and plastic and rubber additives. These products are produced by substitution of the chlorine atoms of the cyanuric chloride by other ligands, for example those containing amine, mercapto or hydroxyfunctions. The reactions are well known in the art and are partly carried out in organic solvents, but to a large extent with suspensions of fine-particle cyanuric chloride in water or an aqueous organic reaction medium.
The aqueous cyanuric chloride suspensions can be obtained by converting the commercially available fine-particle cyanuric chloride powder into a paste in cold water with or without the assistance of wetting agents. Low temperatures slow down the unwanted hydrolysis reaction of the cyanuric chloride. The disadvantage of this method for producing suspensions of cyanuric chloride lies in the difficulties involved in handling bulk materials packed in 50 to 1,000 kg containers. Handling is complicated by the physiological and corrosive properties of the cyanuric chloride.
Accordingly, attempts have been made in the past to use cyanuric chloride in the form of a pumpable melt for the production of aqueous suspensions in the same way as can be done where certain organic solvents are used. To this end, the enthalpy of solidification and the specific heat have to be dissipated between the melting temperature and temperatures of preferably around 0.degree. C. At the same time, the suspension formed must not reach temperatures at which the undesired hydrolysis reaction becomes too pronounced, in addition to which the cyanuric chloride particles have to be as small as possible to enable the subsequent synthesis to proceed quickly and selectively.
Prior art represented by German patent 16 70 731 and German published application 21 62 064 describe processes in which molten cyanuric chloride is sprayed into the vapor space of a stirred reactor partly filled with water. However, the effect of spraying molten cyanuric chloride into a gas space is that cyanuric chloride volatilizing from the melt desublimates in the gas space and forms crusts on the wall of the spray reactor which is not wetted with water. These crusts lead to blockages in the reactor and form lumps in the suspension.
German patents 28 50 242 and 28 50 308 describe a reactor which tapers downwards breast-fashion to an outflow opening and in which a spray nozzle is arranged in the reactor head. A rotating liquid ring is produced in the reactor, the cyanuric chloride melt being sprayed onto the surface of this liquid ring. To avoid caking, the rotational speed selected for the liquid ring is so high that the ring almost completely surrounds the spray nozzle at the cover of the reactor. In terms of control technology, this is difficult to guarantee on a permanent basis in the rough conditions of continuous operation. In addition, this construction provides for only a gradual improvement and, because the liquid ring has to be supported by a correspondingly narrow outflow opening, can only handle suspensions of relatively low concentration.
EP-B 0 094 665 describes a process for the production of a suspension of cyanuric chloride in water or for the reaction of cyanuric chloride in ammonia or amines which is said to avoid most of the disadvantages attending known processes. In this case, molten cyanuric chloride is sprayed into water or an aqueous ammonia or amine solution or suspension by means of a spray nozzle which dips into the liquid. Before the spraying process is started, however, the liquid level surrounding the nozzle is reduced to such an extent that the tip of the nozzle no longer dips into the liquid. The liquid level is only raised again after starting so that the nozzle dips into the liquid again. The above-mentioned problems characteristic of the spraying of molten cyanuric chloride into a gas space are not eliminated in this process either, particularly in the start and stop phases of the spraying process.
In all the processes mentioned above, the injection system, i.e. in particular, the spray nozzle and its feed pipe for molten cyanuric chloride, is prevented from being internally wetted with water during the start and stop phases because otherwise hydrolysis products would be formed from cyanuric chloride residues, blocking the nozzle and contaminating the cyanuric chloride suspension.